Can I undelete a file even if I formatted the drive?

If it was a Quick Format then it is possible if the drive was formatted in FAT format and was previously in FAT format. Most smaller USB keys, smart cards, etc. are formatted in FAT. To list the files you must tick the option Scan empty clusters for deleted files (FAT only) when choosing the drive to scan. It is much slower, but this is because it is looking at every part of the drive for any trace of deleted files.